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Long-duration insurance contracts - Summary of life, annuity and health insurance benefits liabilities (Detail) - USD ($) $ in Millions | Sep. 30, 2025 | Sep. 30, 2024
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Liabilities for Guarantees on Long-Duration Contracts [Line Items] |  |
Life, annuity and health insurance benefits | $ 18,275 | $ 18,612
Periodic Payment Annuity [Member] |  |
Liabilities for Guarantees on Long-Duration Contracts [Line Items] |  |
Life, annuity and health insurance benefits | 10,578 | 11,136
Life and Health [Member] |  |
Liabilities for Guarantees on Long-Duration Contracts [Line Items] |  |
Life, annuity and health insurance benefits | 4,721 | 4,456
Other [Member] |  |
Liabilities for Guarantees on Long-Duration Contracts [Line Items] |  |
Life, annuity and health insurance benefits | $ 2,976 | $ 3,020

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